The course of theological development in ecclesiastical antiquity may in some parts be compared to the windings of a descending spiral. Starting from any given point we seem to be always getting further away, and finally we come back to it again; only we are a stage lower down. The great Trinitarian controversy of the Fourth Century has its starting-point in the Christological doctrine of Paul of Samosata: Christ, the deified man inspired by the power of God and one with God in loving affection and in energy of will. Opposed to this doctrine was the belief that Christ is co-substantial with God, the Θεός ὁμοούσιος, who has become man. This article of faith established itself after Arianism and other middle doctrines had been rejected. But when in the course of the development both the perfect Godhead and the perfect humanity of Christ had been elevated to the rank of an article of faith, it looked as if the unity could be secured only by once more following the path taken by Paul of Samosata, by emphasising the spiritual and moral unity of God and man. This idea of the unity was indeed made more difficult now that the God in Christ had to be conceived of as a personal being, but any other unity no longer offered itself to thinking people who were unwilling to give up clear views on the subject. And it was still permissible to hold this view of the unity; for though the doctrine of Apollinaris had been repudiated, no fixed idea was thereby arrived at as to the nature of the union of the divine and the human. All the conceivable forms in which the conception of 165the union of the divine and the human might be put, were still at anyone’s disposal, especially as no single term was yet in regular use.

As it was the Antiochian Apollinaris who worked out to its logical conclusion the doctrine of the Trinity as regards Christology, so it was his compatriots who worked out to its logical conclusion the formula “perfect God and perfect man.” This conclusion was indeed the opposite of the doctrine of Apollinaris. He had shewn every clear thinker that it was impossible to carry out the idea of the incarnation without deducting something from the essence of humanity, and that the incarnate one could have only one nature (μία φύσις). But if the human nature in the incarnate one was nevertheless to be complete,—and the Church maintained that it was,—then the conception of the incarnation would have to get a new form. And if piety should suffer in the process, well, there was and there still is a stronger interest than that of piety—namely, that of truth.